9.2 Algebra Stability Criterion (代数稳定判据) +G(s The closed loop transfer function is C(S) G(s) H(S) R(S) 1+G(S)H(S) To insure stability we require that the roots of the following characteristic equation are on the left half plane 1+G(s)H(S)=0 Let's assume that the characteristic equation is an n-th order polynomial 1+G(s)H(s)=aoS"+aS"++amS+a And its characteristic roots are 129.2 Algebra Stability Criterion (代数稳定判据） And its characteristic roots are n s , s , s 1 2